Abstract
Cholesterol efflux from cultured cells can be mediated through binding of high density lipoprotein (HDL) to a cell-surface site which shows many characteristics of a biological receptor. To determine whether a specific protein forms a component of this site, cell membrane proteins were analyzed by ligand blotting using 125I-HDL3. Results demonstrated that membranes from a number of cell types possess a protein with an apparent molecular mass of 110 kDa that binds HDL and apoA-I and apoA-II proteoliposomes, but not low density lipoprotein, acetylated low density lipoprotein, or apoE proteoliposomes. The binding activity of this protein was increased by loading cells with cholesterol and was abolished by trypsin treatment of intact cell monolayers. These results suggest that HDL binds with specificity to a cell-surface protein which is regulated by intracellular cholesterol levels. Since HDL binding to intact cell monolayers shows the same characteristics, the 110-kDa binding protein may represent the proposed HDL receptor that functions to facilitate transport of cholesterol from cells to HDL particles.
Highlights
Presented in preliminary form at the 1986 annual meeting of the American Heart Association Council on Arteriosclerosis
The cell pellets were washed twice at bility, and specificity and is up-regulated by loading cells with4 "C with phosphate-buffered saline (PBS) containing 2 mg/ml trypsin soybean inhibitor and unesterified cholesterol [1,2,3,4,5]. These results suggest that the high density lipoprotein (HDL)-induced efflux of cholesterol from cultured cells ismediated through binding of HDL t o a cell-surface site which twice with protein-free PBS, and cell membranes were prepared as described below
The abbreviations used are: HDL, high density lipoprotein; LDL, The concentration of CHAPS was adjusted to below its critical low density lipoprotein; BSA, bovine serum albumin; PBS, phos- micelle concentration (
Summary
Presented in preliminary form at the 1986 annual meeting of the American Heart Association Council on Arteriosclerosis. These results suggest that the HDL-induced efflux of cholesterol from cultured cells ismediated through binding of HDL t o a cell-surface site which twice with protein-free PBS, and cell membranes were prepared as described below.
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